Monitoring the wet processing of a material

ABSTRACT

AFTER MATERIAL LEAVES APPARATUS, SUCH AS A WASING MAAFTER MATERIAL LEAVES APPARATUS, SUCH AS A WASHING MACHINE OR MERCERISER, IN WHICH IT IS WET PROCESSED, THE LIQUID RETAINED BY THE MATERIAL IS REMOVED IN TWO STAGES, E.G., BY TWO SEPARATE PAIRS OF NIP ROLLERS. MOST OF THE LIQUID IS REMOVED IN THE FIRST STAGE. LIQUID REMOVED IN SECOND STAGE IS COLLECTED, AND ITS NATURE, E.G., ITS PH, EXAMINED TO GIVE AN INDICATION OF THE CHARACTERISTICS OF THE MATERIAL. SIGNAL DEPENDENT UPON INDICATION MAY BE USED TO ADJUST ACTION OF THE APPARATUS.

March 2, 1971 I G. J. PARISH 7 I MONITORING THE WET PRQCESSING OF A MATERIAL Filed April 25. 1969 4 f 28heets-Sheet 1 INVENTOR:

G. J. PARISH v March 2 1971 3,567,365 v MONITORING THE WET PROCESSING OF A MATERIAL Filed April 25, 1969 2 Sheets-Sheet i INVENTOR;

United States Patent 3,567,365 MONITORING THE WET PROCESSING OF A MATERIAL Geoffrey James Parish, Manchester, England, assignor to The Cotton Silk and Man Made Fibres Research Association Continuation-impart of application Ser. No. 525,945, Feb. 8, 1966. This application Apr. 25, 1969, Ser. No. 819,165 Claims priority, application Great Britain, July 24, 1968, 35,296/ 68 The portion of the term of the patent subsequent to Feb. 10, 1967, has been disclaimed Int. Cl. D06l1/00 US. Cl. 8142 13 Claims ABSTRACT OF THE DISCLOSURE After material leaves apparatus, such as a washing machine or merceriser, in which it is wet processed, the, liquid retained by the material is removed in two stages, e.g., by two separate pairs of nip rollers. Most of the liquid is removed in the first stage. Liquid removed in second stage is collected, and its nature, e.g., its pH, examined to give an indication of the characteristics of the material. Signal dependent upon indication may be used to adjust action of the apparatus.

This application is a continuation-in-part of copending application Ser. No. 525,945, filed Feb. 8 ,1966, now US. Patent No. 3,494,721.

This invention concerns the wet processing of continuous lengths of material. The term wet process is used herein to mean a process involving treatment with any liquid and is not intended to be restricted to processes where the liquid is water.

The wet process may be a continuous cleaning process of the kind wherein a travelling length of absorbent material particularly textile material is passed through a unit in which it is cleaned by treatment with a suitable liquid for the purpose of removing unwanted substances, hereinafter termed impurities whether such be dirt, or a chemical in the material from a previous treatment process.

In order satisfactorily to control a process of the kind referred to it is necessary to have some means for determining the concentration of impurity in the material after the cleaning treatment. The direct measurement of this concentration in a moving material is extremely difficult and measurements of concentration in solution are much simpler; many techniques for making this type of measurement are, of course, known and these techniques may apply either to continuously flowing solution or to discrete samples.

Methods for the monitoring of cleaning processes of the kind referred to are known which depend on measurements of the impurity concentration in the liquid in the cleaning tank. This type of measurement is unreliable for two reasons. Firstly, the concentration in the tank is generally lower than the concentration on the treated material and bears no fixed relation to it; the ratio of these concentrations depends on the eificiency of cleaning and on the amount of cleaning liquid employed. Secondly, the response of this type of measurement is generally slow, because of the large volume of liquid in the tank.

When the material emerges from the cleaning unit it is of course necessary substantially to remove the cleaning liquid retained by the material from such material and this is usually effected by passing the material through the nip of a mangle.

Measurement of the concentration of impurity in the liquid squeezed from the material at the nip does not suffer from the second disadvantage aforesaid, but experiments have shown that the concentration in this liquid shows the same type of variability in relation to the concentration in the treated material as does the liquid in the cleaning tank.

However, we have found that if a substantial proportion of the liquid is removed from the material before it reaches the nip the liquid then squeezed out at the nip has a concentration very close to that of the liquor retained by the material.

Thus, according to the present invention a method for monitoring a continuous cleaning process of the kind referred to includes the steps of removing the bulk of the liquid retained by the material after leaving the cleaning unit by any suitable means, removing further liquid by any suitable means, collecting the liquid removed at said second means, and measuring the concentration of impurity therein.

The step of measuring the concentration of impurity in the liquid expressed at said second means may be performed either at intervals or continuously.

According to a preferred feature of the invention a signal dependent upon the measurement is obtained which is either fed back to the cleaning unit for the purpose of adjusting conditions therein whereby the cleaning process is controlled automatically or fed to another machine for the purpose of compensating for an undesired characteristic found in said measurement.

The principles of the invention are applicable not only to continuous cleaning processes as defined above, but also to wet processes where a liquid is applied to a continuously travelling length of material for the purpose of introducing an additive to the material which modifies the characteristics of the material, and where the modification is accompanied by a related change in the nature of the liquid content of the material subsequent to the application of the treatment liquid. The term modification is to be understood as not including within its scope the mere extraction from the material of a substance. In the processes I presently have in mind there will be, for example, a chemical reaction causing the modification, or some change in, say, the concentration of a substance carried in liquid solution by the material.

Broadly speaking, therefore, according to the present invention, a method of monitoring or controlling a wet process of the type described includes the steps of applying the treatment liquid to the material whilst travelling, later removing the bulk of liquid contained by the travelling material, and still later removing further liquid from the travelling material, collecting the last liquid, and by examining its nature, assessing the characteristics of the material with which the process is conceried. Preferably a control signal will be produced, if, as a result of that assessment the characteristics are found not to be as required, and that control signal is used to cause a corrective variation in the applied liquid or in some other processing condition.

Also, according to the present invention apparatus for carrying out such a process includes means for applying a treatment liquid to a material whilst travelling, means for later removing the bulk of liquid from the material, means for still later removing further liquid from the travelling material, means for collecting said further liquid, and means for continuously or intermittently examining the nature of said further liquid whereby the characteristics of the material with which the process is concerned may be assessed.

Reference will be made hereinafter to the accompanying drawings, in which:

FIG. 1 shows, by way of example only, in diagrammatic form, one form of apparatus for practicing the invention in connection with a commercial washing process; and

FIG. 2 shows, by way of example only, in diagrammatic form, an apparatus used for a treatment following the mercerisation of a textile material in a continuous length.

The principles upon which the invention is based will be further apparent from the following tables which relate, by way of example only, to the removal of sodium chloride from a plain cotton cloth of 3.7 ounces per square yard.

In the experiments upon which the tables are based, samples of cloth were passed through a solution of sodium chloride for the purpose of impregnating same. Samples of impregnated cloth were washed with different severities. After washing, the cloth samples were led through two consecutive nips, the first to remove the bulk of the wash liquor from the material, the second to remove further liquor.

In the tables the impurity concentrations are given as grams of NaCl per litre of solution, and liquor retentions are expressed as percentages based on the over-dry weight of the cloth.

Table I relates to cloth liquor and wash tank liquor, Table II cloth liquor and total nip liquor (that is the liquor from both nips) and Table III cloth liquor and second nip liquor after preliminary squeeze.

The results in Table I show that the impurity concentration of liquor retained by the cloth bears no constant relationship with that of the wash tank liquor.

The results in Table II show that the concentration of impurity in the liquor retained by the cloth bears no constant relationship with that of the total nip liquor.

The results in Table III show that the concentration of impurity in the liquor retained by the cloth bears a substantial constant relationship with that of the liquor removed at the second nip.

The results in Table II show levels of liquor removal at the nip which are unsatisfactory and Table II shows some levels of removal at the second nip that are satisfactory.

In our experiments with two nips, the nips have been so positioned that a time interval of about 3 to 6 seconds elapses between the two squeezings.

The liquor squeezed out of the main or second nip is collected in a tray beneath the nip rolls. To prevent the liquor from running back down the cloth and not reaching this tray the cloth must approach the nip from a higher level.

The results in the tables give impurity measurements as concentrations in the respective liquors. Some impurities are preferentially retained by the cloth (a good example is caustic soda or cellulose). In these circumstances the cloth, after squeezing, in addition to carrying contaminated liquor also holds some impurity more or less loosely bound to itself. The relation between the concentration in the nip liquor and the total impurity level on the cloth is then one of equilibrium, where equilibrium is the state that would be reached after prolonged contact between cloth and solution. The relative concentrations in this state can be determined beforehand by simple laboratoryscale tests.

TABLE I Impurity concentration, g. NaCl per 1. solution TABLE II Impurity concentration, g. N aCl per 1. Liquor content of cloth,

solution percent of dry cloth weight In liquor 5 In liquor removed at, retained Before After Removed both D by cloth nips nips at nips TABLE III Impurity concentration, g. NaCl per 1. Liquor content of cloth solution percent of dry cloth weight 1 5 In liquor After After Removed In liquor removed at retained first second at second second nip by cloth nip nip nip It is thought that the techniques of monitoring a cleaning process of the kind referred to in accordance with the method of the invention could be usefully practised in many different fields, amongst which may be mentioned the washing of fabrics for removal of dirt, the scouring of fabrics after bleaching, desizing and removal of excess dye, for example.

The bulk of liquid may be removed from the material on leaving the cleaning unit by any suitable means, for example, by use of a nip, a suction means or a doctorblade or like means.

Further liquid may be removed by a nip or any other suitable means collected for measurement of the impurity therein, and such measurement may be effected at intervals or continuously.

A suitable signal may be produced and fed either back to the cleaning unit to adjust the treatment conditions therein whereby the cleaning process is controlled automatically, or fed to another machine for the purpose of compensating for an undesired characteristic found in said measurement.

As can be seen in FIG. 1, a length of textile fabric F is passed through a conventional washing machine M in known manner. The fabric leaving the machine passes through a first nip N comprised by a pair of bowls or rollers where the bulk of the liquor retained by the fabric is squeezed therefrom, collected and returned to the washing machine. The fabric is then passed through a second nip N where further liquor is squeezed from same. This further liquor is collected by a trough T and passed through a measuring instrument I which gives a continuous eiectrical output signal whose magnitude is proportional to the concentration of impurity in the liquor sensed by the instrument I. This signal may be used either to control conditions in the washing machine M or to modify the conditions of a further processing of the fabric F as for example further washing machines in a washing range. It will be noted that the provision of guide rolls between the two nips ensures a time interval between the two squeezings enabling conditions on the fabric to tend towards an equilibrium before the second squeezing.

Another embodiment of the invention will be described with reference to FIG. 2. Inv one example of a mercerising process the fabric is rinsed on the merceriser, to remove the bulk of caustic soda, passed through an acid bath and rinsed again. The material leaves the mercerising range in an acid condition and a separate operation is passed through a washing range, which consists, successively, of a rinse bath 10, a neutralizing bath 11, a second rinse bath 12, and a third rinse bath 13. Between each bath the fabric F passes through a nip 10a, 11a and 12a, respectively to prevent excess liquor from the baths being transferred from one bath to the next. After bath 13 the fabric passes through a pair of squeeze nips 14 and 15. The first nip 14 is removing the bulk of liquid from the cloth, and the second nip 15, for removing a continuous sample of further liquid as described above. This sample passes via a collecting trough 16 to a conventional pH electrode 17. The pH electrode 17 is fitted with a limit switch (not shown) which energises a control circuit C when the pH falls below the set point. The control circuit C then operates the flow-control valve 18 to allow a pre-determined amount of alkali stock solution to enter the neutralizing tank 11 via conduit 19. The required concentration of alkali in this tank 11 will depend on the acidity of the incoming fabric; a higher acidity will normally require a somewhat greater alkali concentration. The control arrangement ensures that the concentration reaches the value necessary to achieve the desired pH at the measuring point; i.e. in the liquor collected from the emerging fabric at the second squeeze nip. The type of control circuit employed is not critical. A limit switch and a sampled-data controller 20 are envisaged, but a conventional proportional or proportional/integral controller could be used.

In an alternative arrangement an analogous control system could be used in the mercerising range itself to control the feed of acid so that the fabric comes off in a substantially neutral state.

Either of these alternatives provides essentially single sided control, that is to say it can control only to an acid or an alkaline limit. It would be feasible to have two-sided control with feeds of both acid and alkali, fed into the same or different tanks.

A similar control could be applied where an added chemical reacts in some way with a substance present in or previously applied to the material; or in fact with the material itself, as for example, in the case of a bleaching process. It is only necessary that the extent of the reaction should be measurable in the liquor removed at the nip, for example by a continuous or semi-continuous titration process.

The procedure could also in principle be used to control the addition of a chemical without any chemical reaction, if the amount of this chemical were measurable in the nip liquor. A reasonable application would be to a situation where the liquor on the fabric is difierent in concentration from the liquor in an impregnation tank (for example, because of water initially held by the fabric).

Although reference has been made in the example given above to the passage of the material through a tank for the application of the liquid thereto, other methods of application are possible. Thus, for instance, the liquid could be sprayed on, and the spray rate could then be controlled.

What we claim is:

1. A method of monitoring a wet process of the kind wherein a travelling length of absorbent material has a treatment liquid applied to it, comprising the steps of removing the bulk of the liquid carried by the material, thereafter removing further liquid carried by the material,

measuring some identifiable property of said futher liquid, and producing a signal which is a function of the measured property.

2. A method according to claim 1 comprising the further step of using said signal for control purposes.

3. A method according to claim 1 wherein the step of measuring some identifiable property of said further liquid is carried out at intervals.

4. A method according to claim 1 wherein the step of measuring some identifiable property of said further liquid is carried out continuously.

5. A method according to claim 1 wherein the step of measuring some identifiable property of said further liquid comprises contacting a pH electrode with said further liquid, said signal being produced by a variation in the pH of said further liquid from some predetermined set point.

6. A method according to claim 1 wherein the identi fiable property measured is the acidity or alkalinity of said further liquid.

7. A method according to claim 1 wherein said signal is used to control the application of a chemical to said material which chemical reacts with a substance carried by the material.

8. A method according to claim 1 wherein said signal is used to control the application of a chemical to said material which chemical reacts with the material itself.

9. A method according to claim 1 wherein said signal is used to control the application of a chemical to said material which chemical reacts neither with a substance carried by the material nor with the material itself.

10. A method according to claim 1 wherein the identifiable property measured is the difference in concentration of some substance in the further liquid and in the treatment liquid.

11. A method according to claim 1 wherein each of the bulk and further liquid is removed from the material by passing the latter between a pair of rotary cylindrical members.

12. A method according to claim 5 wherein said signal is used to operate a flow control means for controlling the flow of a stock liquor with which the material is treated.

13. A methd according to claim 6 wherein said signal is used to alter the treatment liquid to maintain the pH of the material within a predetermined range.

References Cited UNITED STATES PATENTS 2,223,860 12/ 1940 Schellenberg 8l37X 3,093,442 6/1963 Brown et al. 8142 3,101,239 8/1963 Warren et al. 8142 3,101,240 8/1963 Mathews 8142 3,160,317 12/1964 Hambro 8142X MAYER WEINBLATI, Primary Examiner U.S. Cl. X.R. 8137, 147 

